Process of making wax patterns



. INVENTORS Paul S. McFadden 8 Warren L. Marshall. BY Q A/TTRNEY FiledJune 21, 1951 P S MCFADDEN IAL PROCESS OF MAKING WAX PATTERNS Oct. l2,1954 Patented Oct. 12, 1954 A'reiu'rfA A0.111111'ce:I.

PROCESS OF MAKING WAX PAT'1ER`N"S"`l Application'JuneZl; 1951:,Seriali-No2 232579361! This: invention relates to -themaking oif'wax:`p'atternsffor` use in precision casting.:

I-n I practicing. precision.v casting. it has: been the: custom to makeWax. patterns of the article. tobe: produced, invest the pattern in a.suitablezin'vestment' material'and-.thereafterto melt the. wax:pattern'l from the investment. material' to. leaf/ey acasting mold forlreceiving. molten metal; lWhere the article to be produ-cedV is small,there has. been no particular problem in producing thezwaxf. patterns.However, wherethearticle is large, the shrinkage-of the waxpattern. asthe wax cools inv the injection mold or die presents` a difficultVproblem, making it substantiallyl impossible` to hold rigid dimensionaltolerances'.

Recently thereV has been developeda proc'essrofl employing a steel corevin` a diei cavity having the configuration of the article toV beproduced sol as# to reduce the amountoffwaxusedfinformingthe pattern andtherebyf attempt to control or limit the shrinkage oi-the wax formingthe pattern. In such a process; after theA wax-wasl injected about the'steel .core in thedie cavity and solidiedr, thersteel core was removedfrom the wax pattern necessitating a manual sea-ling of the. openingleft therein' by withdrawing the` steel core;

Suchy aprocess of making thef wax' patterns has not proven to'besatisfactory for a number' ofY reasons: The steel core must` berelatively straight with.` a' slight taper to permitV stripping of thecore, from the waX pattern. Each core' member' mustbe mounted' onV abase blockA with the. result.y that they are: not' always identicallymounted. .and :the patterns formed. are not; iden-- tical` as. to wallthickness-f.and the like'. Further; when: a steel. core is removed from.the waxlpattern the. void. or cavityleft by the removal of the: steel'corepermits collapse-of the pattern' and in all cases such voids'must`be manually sealed` bey fore the patterns lcan Vbe used.

An'r object of this invention =is to provide' a processof making asubstantially -solidwaxf pat-- tern of relatively large.l size. havingrigid dimen-Q sional tolerancessvl Otherobjects of' this invention willbecomeapparent` from` the.following description when taken: in.4conjunction with: 1 the# accompanying drawing;.in which;A

Figure 1i isv a' view inf section of a die hav-ingr a1 wax patternlformed thereinin: accordance with: theteachin'gszotthisinventiongf andVFig. 2 is a: vievfin section.' of fa:v waxlpattern: of' theturbineiblade formedrby' the process' :of this:v invention.` t

Referringfto thedrawfinggthis'invention isy illustratedfbyreferencerto'theimaking ofi'awax pat-e* tern: of `a turbine blade. vIn.rpracticing the? infventiun, a split mold or die: l0 is termed having. adie cavity i2 thereiny of; the configuration andr size ofthe article, in.this `case a turbine-blade; which-v istc--beproduced. Inr-thef-caseoia;turbine; blade; the die' cav-ity- I2. is formed withf` a root. section Iicorrespondingt'o the roots section of: the turbine bladeftolie-.produced The: dial-liais-v also providedf'with a gate' I tflocated.at. any convenient point andin` the: example illustrated the gate ISyis-illustra'ted as;supplying; the root section Moi the cavityiZ;

In accordancewvith-this invention,acorememef ber'llty is. rst formedi(3f-waxA A1 waxy-compost tion z suitable for "making the :core member,anda the resulting was: pattern.y is that disclosed' antl-v claimed:in" PatentZAG'lqlQSfissued: Aprilvlfg;` 1949;, to B.,Willisand=assignedstof-thefzassigneeor this invention. 4'I-'he core membersI8." may-i be: formed;l in anyA 'suitable4 manner; oner modef 'beingthat disclosed in-A Patent 2,934,557; issued J anuary 13, 1948;..to-Foxetral'. andassignedtothefase. signez-)Hof .this-v invention,Inpracticarthecore member lit-preferably has substantiallyl the-f sameconfiguration asthe.- nal,` waxpatternr which.:y isv to be producedalthough the Vcorev memberi t8 .is much smallerl in: size. rthe.coref'member i8'- may be` said. .toconstitute a miniature-,ot thewairpattern whichfis'tobernaHy produced; i

Asillustratedthe example shown finr thef drawing, Athe core :member:4 i8isfprovidedi-withf substantially the conguration of the die cavityf t2','butisr much. smal-lerfs'o .asit'oi provide at space Z between the:core' member: and' the walls off the? diet cavityvr IfZiIWh'err thecore.memberA |18' is? in'-i serted therein-,which space 2U issubstantially uniforml throughout" thedie cavityfv l2; InpreuzV` tice,thefcore member I`8is preferably formed withk a base po1'tion-22.which'corresponds 'to-fa` part of'` .the final rootsectionof the pattern tovbe formedl and aA part .or-'the rootl section '-M- ofthe cavity-i l2formedl in the' die" llli 'i By'f'fformi'ng thev core' memberv I 8 ofwax'intm`smanner; tlie' core ymein- A ber` can bereadilypositioned; inthe'- diefl il as' thel root portion: 22" of the' core' member' A'I 8vinto thefcorrespond-ing portion' of the-rootsection `M" ofth'e 'cavity22 'effectively sealing the' cavityY and?L maintaining the" core:`membersl If. in kposition; spacedv from .the walls ofi the die cavi-ty?I 2.v if

Witl'r the?v core-fm'en'uber .I'Bi .positioned this: mannerin the' die`cavityfi lf2", additional'- wazc vis injected -intofztlre7 dien'.cavity: through:- vthe: gate" |16; lin any suitable:manner'andf-preferablyf irrtlr'e-T manner disclosed in the Fox et al.Patent 2,434,557 referred to hereinbefore. Thus the additional waxinjected into the die cavity I2 is in a plastic condition having atemperature ranging from between 55 C. and '70 C. whereby when injectedunder pressure into the die cavity, the plastic wax flows smoothly andfreely into the cavity I2 without excessive turbulence to flow about theWax core member I8 and completely fill the space 20 between the coremember I8 and the confines of the die cavity I2. It is thus seen thatthe plastic wax also completely iills the remaining portion of the rootsection I4 of the cavity I2 and interlocks with the base portion of thecore member I8 and since the core member I8 has substantially the sameconguration as the single wax pattern, that is, it is provided withcurved surfaces, the injected wax iiows about the curved surfaces toeffect interlocking of the injected wax with the core mold I8.

When the die cavity I2 is thus iilled, the injected wax is cooled andsolidified in interlocked relation with the core member I8 so that asubstantially solid wax pattern 24, as shown in Fig. 2, results. Inpractice, the temperature drop in the mold or die I!) is usuallysufcient to effect the cooling of the injected plastic wax when thecavity is filled so that the injected wax will solidify in positionabout the core member I8. Where desired, forced cooling of the die Itmay be eected to accelerate the cooling of the injected wax althoughthis is not usually necessary.

After the cavity I2 is thus filled and the injected wax is solidified ininterlocked relation with the core member I8, the die l0 is removed fromthe injecting apparatus, for example, that shown in the Fox et al.Patent 2,434,557, and the die is opened and the wax pattern 24 removedtherefrom. The resulting pattern 24 is a dupli cation of the mold cavityI2 and since only a portion of the wax of the final pattern 24 has beeninjected into the mold, it is found that variation in the shrinkage ofthe wax upon cooling is substantially eliminated, the dimensionaltolerances of the die cavity being maintained in the resulting pattern.Since the wax injected into the die cavity I2 is in the plasticcondition, no melting or distortion of the wax core member I8 is foundand in fact if the final wax pattern 24 is broken, it is quite evidentthat the core f member retains its true identity in the final product asthere is no adherence due to melting between the core member I8 and theinjected Wax.

As is quite evident, the wax pattern 24 thus produced needs no furthermanual treatment other than to mount it for assembly in a flask forinvesting the pattern with a refractory investment material. The factthat a wax core is utilized provides for uniformity of the resulting waxpattern since the entire pattern is formed of wax. Further, since thewax core members can be made from a single master pattern, the Wax coremembers are uniform in shape and size, making it possible to duplicatethe positioning of the wax patterns in the die cavity in the making ofthe final Wax pattern. The size and shape of the core member la will, ofcourse, depend somewhat on the final Wax pattern to be produced althoughit is desired in all cases to provide the core member with a non-uniformbase portion to facilitate interlocking of the injected plastic wax withthe core member. Preferably, the core member also is provided ofsubstantially the same configuration as the final Wax pattern so that asubstantially uniform spacing may be obtained between the surfaces ofthe core member and the die cavity in which the core member is mounted.

By forming the wax pattern 24 in the manner described hereinbefore, itis evident that distortion of the wax pattern during stripping of thepattern from the die member is substantially eliminated since the waxpattern is a solid wax member. Further distortion of the wax pattern,such as was encountered where a steel core member has been utilized, hasbeen completely eliminated since it is no longer necessary to strip thecore member from the nal wax pattern. Likewise, since it is no longernecessary to remove the core member from the final wax pattern 24, suchWax pattern is completely free of voids so that the danger of collapseof the Wax pattern during handling or investing procedures is alsoeliminated. Considerable savings are effected by the process of thisinvention as such process also eliminates manual handling of the iinalwax pattern for sealing the voids such as was necessary in the prior artprocesses.

It will, of course, be appreciated that While reference has been made toone type of wax composition, other wax compositions may be employed inpracticing the process of this invention. Likewise, different apparatusmay be utilized for forming the core member Iii and for injecting theplastic wax into the die cavity of the die IG. However, regardless ofthe type of wax or the apparatus utilized for effecting the ejection ofthe plastic wax, it is quite apparent that the process of this inventionis highly eiiicient and makes possible the production of largequantities of wax patterns with very few rejects while at the same timeeffecting economies in the production of the Wax patterns.

We claim as our invention:

l. In the process of making a Wax pattern to be used in precisioncasting, the combination of steps comprising making from a given waxcomposition an initial core member of predetermined shape smaller thanbut of matching configuration to the desired pattern, placing the coreniember within a hollow die having Walls forming a cavity correspondingto precisely the desired pattern, one end of the core member fittingtightly against the walls of the hollow die whereby to hold the coremember in position and the remainder of the core member is spaced fromthe walls of the die so that there is a relatively small space betweenthe core member and the walls of the die, injecting an additional amountof the same wax composition to fill the space between the core memoerand the die Walls, the additional wax flowing about the core member asit is injected to bond thereto and to cooperate therewith to produce asubstantially solid pattern having the precise conguration of the diecavity, withdrawing the pattern from the die, investing the pattern in arefractory and then heating the invested pattern to melt out all the Waxcomposition thereby leaving a cavity in the investment corresponding tothe wax pattern.

2. In the process of making a precision casting of a blade having a rootsection, the combination or steps comprising making an initial coremember of a given wax composition, the

core member being smaller than the desired blade, but having a rootsection substantially of the desired final shape, positioning the coremember in a die having walls forming a cavity corresponding to the exactdesired blade shape,

the root section engaging with the corresponding portion of the diewalls to hold the core member in position so that a small space ispresent between the rest of the core member and the die walls, injectingan additional amount of the same wax composition into the die cavity toow about and to bond with the core member and to fill the die, coolingthe wax composition, withdrawing the resulting Wax pattern from the die,investing the wax pattern in a refractory, and then heating the investedpattern to melt out all the wax composition thereby leaving a blade 6cavity in the investment corresponding to the configuration of the diecavity.

References Cited in the le of this patent UNITED STATES PATENTS NumberName Date 1,313,907 Petry 1 Aug. 26, 1919 1,675,732 Schweitzer July 3,1928 2,136,404 Wheeler Nov. 15, 1938 2,420,851 'Zahn et al. May 20, 19472,532,280 Atkinson Dec. 5, 1950

